1. Field of the Invention
The present invention relates to suitable manufacturing method for an image-forming apparatus using an electron beam such as a field emission display (FED) or cathode ray tube (CRT), for example, and a face plate used in such an image-forming apparatus.
2. Related Background Art
There is a demand for much larger image-forming apparatuses such as CRTs, and a great deal of research is being carried out in this regard. As size increases, achieving thinness, light weight, and low cost of the apparatus have become major concerns.
However, as the structure of a CRT is such that electrons accelerated by a high voltage are deflected by deflecting electrodes, and irradiate a phosphor on the face plate, causing excitation, when the size is increased, depth is necessary in principle, making it difficult to achieve thinness and light weight.
The inventor has been conducting research into an image-forming apparatus using surface conduction electron-emitting devices, as an image-forming apparatus capable of solving the above described problem.
Application to a multi-electron-beam source of an electron-emitting device by means of an electrical wiring method such as that shown in FIG. 4 are disclosed in U.S. Pat. No. 5,936,342, U.S. Pat. No. 5,451,835, and WO 00/44022, etc.
The apparatus shown in FIG. 4 has a 2-dimensional arrangement of a plurality of surface conduction electron-emitting devices, and, as shown in the figure, these devices constitute a multi-electron-beam source wired in simple matrix form. FIG. 4 shows a circuit diagram for the case where surface conduction elctron-emitting devices are connected by matrix-wiring.
In the figure, reference numeral 4012 schematically indicates a surface conduction elctron-emitting device, reference numeral 4002 indicates column-directional wiring, reference numeral 4003 indicates row-directional wiring, and reference numeral 4004 indicates resistances.
For the purposes of illustration, a 6xc3x976 matrix is shown, but the scale of the matrix is not, of course, limited to this: as many devices as are sufficient to perform the desired image display are arrayed and wired.
FIG. 5 shows the structure of a flat type cathode ray tube using this multi-electron-beam source.
In FIG. 5, surface conduction electron-emitting devices 4012 are provided on a substrate 4001, and the structure consists of a rear plate 4005 and side wall 4007, a face plate 4006 provided with a phosphor layer 4008, and an electroconductive film (so-called metal back) 4009 on the phosphor layer.
The configuration is such that a high voltage is applied to the metal back 4009 from a high voltage power supply 4010 through a high voltage input terminal 4011.
In order to output the desired electron beams, in the multi-electron-beam source in which surface conduction electron-emitting devices 4012 are simple-matrix-wired, appropriate electrical signals are applied to the column-directional wiring 4002 and row-directional wiring 4003.
For example, to drive an arbitrary row of surface conduction electron-emitting devices within the matrix, a selection voltage Vs is applied to the row-directional wiring 4003 of the selected row, and at the same time a non-selection voltage Vns is applied to the row-directional wiring 4003 of the non-selected rows.
In synchronization with this, a drive voltage Ve for outputting electron beams is applied to the column-directional wiring 4002.
According to this method, voltage Vexe2x88x92Vs is applied to the surface conduction electron-emitting devices of the selected row, and voltage Vexe2x88x92Vns is applied to the surface conduction electron-emitting devices of the non-selected rows.
If the size of these voltages Ve, Vs, and Vns is adjusted appropriately, an electron beam of the desired intensity is output only from the surface conduction electron-emitting devices of the selected row, and if a different drive voltage Ve is applied to each column-directional wire, electron beams of different intensity are output from each device of the selected row.
As the response speed of the surface conduction electron-emitting devices is fast, by changing the length of time for which the drive voltage Ve is applied, it is also possible to change the length of time for which the electron beam is output.
By means of the above described voltage application, the electron beams output from the multi-electron-beam source configured by surface conduction electron-emitting devices are applied to the metal back 4009 to which a high voltage Va is being applied, pass through the metal back 4009, strike the phosphor of the phosphor layer 4008, which is a target, and excite the phosphor, causing it to emit light.
Therefore, the image-forming apparatus shown in FIG. 5 becomes an image display apparatus by appropriately applying voltage signals corresponding to image information, for example.
Thus, the above described image display apparatus displays an image by applying a high voltage to the metal back 4009, generating an electric field and accelerating electrons between the rear plate 4005 and the face plate 4006, and exciting the phosphor, causing it to emit light.
Meanwhile, in order to realize a drastically thinner image display apparatus, it is necessary to reduce the distance between the rear plate 4005 and face plate 4006 shown in FIG. 5, for example.
Therefore, a considerably higher field strength arises between the rear plate 4005 and face plate 4006 than in the case of a CRT. Also, the higher the acceleration voltage, the stronger is the light emission and the greater the brightness of the image display apparatus.
The metal back 4009 is generally configured by a metal film. The reasons for this are to enable a high voltage to be applied to the entire phosphor layer, to remove charge by the metal back from the phosphor which is an insulator, and also to enable light emitted from the phosphor toward the rear (in the direction of the rear plate) to be conveyed (reflected) toward the front by means of a mirror-surface effect. It is therefore necessary for the metal back to be a continuous film with a certain degree of thickness.
As the accelerated electron beams must excite the phosphor through the metal back 4009, the thickness of the metal back 4009 is limited, although this also depends on the potential applied to the metal back.
Meanwhile, as the phosphor is generally a powder, the phosphor layer 4008 is porous and its surface has a considerable number of irregularities.
There are also a considerable number of irregularities on the surfaces of black members (such as the black matrix) provided for such reasons as preventing color mixing of the phosphor, preventing color shifting even if the beam position shifts a certain amount, and improving the image contrast by absorbing external light.
So, it is difficult to produce a continuous metal film directly on the phosphor layer with desired thickness, and so a filming step is generally used as the metal back creation step.
In this filming step, an acrylic or similar resin film is disposed on the surface of the phosphor layer, etc., and the surface of the phosphor layer, etc., is made flat. On the flattened film (resin film), a metal film is formed by means of vacuum evaporation, etc., and then the resin film is thermally decomposed and eliminated by baking, as a result of which the metal film is attached to the phosphor layer, creating the metal back.
As the above described resin film undergoes thermal decomposition and elimination by baking after the metal film is disposed, the resin film becomes a gas, and holes through which that gas escapes are created in the metal back (metal film) (see FIG. 13). In FIG. 13, reference numeral 4006 denotes the face plate, reference numeral 2 denotes phosphor particles, reference numeral 3 denotes the metal film (metal back), and reference numeral 104 denotes protrusions formed around the holes created in the metal film (metal back). In many cases, the thicker the metal film (metal back) formed on the resin film, the more severe is the shape of these holes and protrusions 104.
However, in the case of the related background art as described above, there is a problem in that the strength of the field between the rear plate and face plate becomes high, and spark discharge may occur between the two electrodes, resulting in a deterioration in the quality of the image displayed by the image display apparatus.
With regard to the above described problem, the above described related background art will be described as an example. As stated above, spark discharge may occur when the strength of the field between the rear plate 4005 and face plate 4006 becomes high.
In this case, when the sparking voltage at which spark discharge begins to occur traverses a high-vacuum gap, the material and surface state of the electrodes have an influence.
Consequently, if the metal back has holes and protrusions, as described above, discharge between the face plate and rear plate may be induced. Also, structurally weak protrusions around holes in the metal back, etc., may fall on the rear plate side due to Coulomb""s force, etc., and shorting may occur between the wires laid out in a high-density arrangement on the rear plate side.
One cause of this kind of problem lies in the holes formed in the metal back because of the use of the above described resin film, and the protrusions 104 formed around the holes, as described using FIG. 13. Consequently, when the above described holes and protrusions are created, the idea may be conceived of reducing the thickness of the metal film (metal back) formed on the resin film and decreasing the holes and protrusions 104 due to gas escape. However, there have been cases where, when the metal back is made thinner in this way, there is a drop in the conductivity of the metal back itself, or the original purpose of the metal back in reflecting light emitted from the phosphor toward the face plate can no longer be fulfilled.
Therefore, from the viewpoint of reliability and life, in practical applications the voltage applied to the metal back must be reduced, resulting in the problem of lower image quality as an image-forming apparatus, due to reduced brightness, etc.
The present invention has been implemented taking into account the actual problems described above, and it is an objective of the present invention to provide a face plate manufacturing method and image-forming apparatus manufacturing method that enable bright, high-quality images to be formed stably over a long period.
In order to achieve the above described objective, the present invention provides a manufacturing method for an image display apparatus that comprises a first substrate, a second substrate located at a distance from and opposite the above described first substrate, electron-emitting devices arranged on a principal surface of the above described first substrate, a phosphor film, and an electroconductive film covering that phosphor film, wherein the phosphor film and the electroconductive film are located on a principal surface of the above described second substrate so as to be opposite the above described electron-emitting devices, the method comprising the following steps of:
(A) forming the above described phosphor film on the principal surface of the above described second substrate;
(B) forming a first electroconductive film covering the above described phosphor film;
(C) placing an electrode at a distance from the above described first electroconductive film;
(D) applying a voltage between the above described first electroconductive film and the above described electrode; and
(E) forming a second electroconductive film on the above described first electroconductive film.